DENVER (AP) — A Colorado dentist accused of killing his wife by lacing her protein shakes with poison is set to enter a plea in court to a first-degree murder charge on Tuesday.

Police said James Craig, who began an affair before his wife’s March 18 death, had searched online for answers to questions such as “is arsenic detectable in an autopsy?” and “how to make murder look like a heart attack.” In the following days, Craig’s wife, Angela Craig, then Googled symptoms she was having including vertigo, shaking and cold lips, said District Attorney John Kellner at a July preliminary hearing.

Angela Craig, a mother of six who was married to her husband for 23 years, died of poisoning from cyanide and tetrahydrozoline, the latter a substance found in over-the-counter eye drops, according to the Arapahoe County coroner Kelly Lear. .

At the preliminary hearing, James Craig’s attorneys argued there was no direct evidence that Craig had slipped poison into his wife’s shakes and accused the lead detective of bias against Craig. Neither the affidavit nor testimony during the hearing addressed how investigators believe Angela Craig was poisoned with tetrahydrozoline.

Craig also was later charged with tampering with evidence but details about that allegation have not been disclosed.

The defense attorneys suggested that Craig, who had previously attempted suicide, had been searching online for ways to kill himself. The case’s lead investigator, Bobbie Olson, acknowledged at the preliminary hearing that testing didn’t find any sign of cyanide or arsenic in two bottles used for shakes.

Investigators allege that Craig, who routinely made protein shakes for his wife, tried poising her shake on March 6 with arsenic. After she survived, Craig ordered a rush shipment of potassium cyanide that he told the supplier was needed for a surgery, according to court documents.

The arrest affidavit said that the investigation into Craig started after his dental practice partner mentioned to a nurse that Craig had ordered potassium cyanide even though they didn’t need it for their work.

Police claim Craig was seeing another woman as his wife was being treated in the hospital. But the woman told ABC’s GMA she didn’t willingly have a relationship with someone who was married.

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Bedayn is a corps member for the Associated Press/Report for America Statehouse News Initiative. Report for America is a nonprofit national service program that places journalists in local newsrooms to report on undercovered issues.